Preliminary Report: The Hector Mine Earthquake, 10/16/1999

A M7.0 earthquake occurred at 2:46 a.m. local time on 10/16/1999.
The event was located in a remote, sparsely-populated part of the
Mojave desert, approximately 47 miles east-southeast of Barstow and 32 miles
north of Joshua Tree. The event is not considered an aftershock of the
M7.3 Landers earthquake of 1992, although subsequent analysis will
explore the relationship between these two events.
Preliminary results do indicate that the Hector Mine Earthquake occurred
in a region where stress was increased by the 1992 Landers earthquake.

On average, an earthquake of M7.0 is expected to generate
approximately seven aftershocks of M5 or larger within the first week.
The largest early aftershock was a M5.3 event at 2:49 local time.
A M5.8 aftershock occurred at 5:57 a.m. local time with an epicenter
approximately 15 kilometers south of the mainshock. A third event
with M5.0 occurred at 10:38 a.m.
As of noon on 10/16, 18 aftershocks of M4 or larger have occurred.

The earthquake occurred near the Pisgah fault, which strikes north-northwest
through the eastern Mojave shear zone. Scientists with Caltech and the
US Geological Survey are continuing to analyze the data to determine
whether or not this fault was associated with the earthquake. Geologists
are heading to the epicentral area to look for surface rupture, which is
expected for an earthquake of this magnitude.
(Updated 12:05 p.m., 10/16/99)